J. Tian et al., Borane-functionalized oxide supports: development of active supported metallocene catalysts at low aluminoxane loading, J MOL CAT A, 144(1), 1999, pp. 137-150
Treatment of hydroxylated silica or alumina with tris(perfluorophenyl)boran
e (1), bis(perfluorophenyl)borane (2) or bis(perfluorophenyl)boron chloride
(3), provides borane-functionalized supports of variable composition, as r
evealed by in situ monitoring by F-19 NMR spectroscopy and/or elemental ana
lysis. These chemically treated supports can be impregnated with Cp2ZrMe2 t
o provide supported catalysts for ethylene polymerization. Although some of
these supported catalysts are active for ethylene polymerization in the pr
esence of alkylaluminum compounds (e.g., TMA, TIBAL), all of these catalyst
s are more efficiently activated in the presence of small quantities of met
hyl aluminoxane, even at very low Al:Zr ratios of 10:1. The polymer propert
ies are quite similar to those produced using the soluble catalyst Cp2ZrMe2
/B(C6F5)(3), again in the presence of MAO at low loading. A variety of expe
riments suggest that minimal leaching of the metallocene complex from the s
upport occurs under the conditions studied; in particular, production of po
lyethylene with high bulk densities (> 0.2 g/cm(3)) and little reactor foul
ing, even at elevated temperature in toluene slurry, is observed. (C) 1999
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